The invention relates to a telecommunication network comprising a main station coupled to a plurality of sub-stations over a channel, the main station comprising a distribution modulator for modulating on a distribution carrier a combination of a plurality of distribution signals modulated on distribution subcarriers, each sub-station comprising a return modulator for modulating on a return carrier a return signal modulated on its own return subcarrier.
The invention likewise relates to a main station and a sub-station to be used in a telecommunication network defined above.
A telecommunication network according to the opening paragraph is known from the journal article "Wide-Band Lightwave Distribution System Using Subcarrier Multiplexing" by T. E. Darcy et. al. in IEEE Journal of Lightwave Technology, Vol. 7, No. 6, June 1989, pp. 997-1005.
Such transmission systems are used for communication between a main station and a plurality of sub-stations over a channel used in common by the sub-stations. This channel may be formed, for example, by a glass fibre, a coaxial cable or a radio link. Applications of such transmission systems are, for example, passive optical networks, local area networks, satellite communication systems and mobile telephone systems.
In telecommunication networks utilizing a common channel for all the sub-stations it is to be ensured that no or only little mutual interference is caused by sub-stations simultaneously transmitting information to the main station.
Generally, this may be achieved by giving the signals to be transmitted by the sub-stations their own frequencies, so that at the main station, for example, by means of frequency selective filters, the signals coming from different sub-stations may be separated. Another option is making a different time slot in a frame available to each sub-station, so that only a single sub-station at a time transmits a signal to the main station.